Counter-rotating electromagnetic generator with planetary gear amplification for low-frequency wave energy harvesting

Ocean wave energy represents a promising renewable resource with high energy density. However, its inherently low-frequency, stochastic, and multi-directional characteristics pose significant challenges for efficient energy harvesting. In this study, a pendulum-type counter-rotating electromagnetic generator (CREMG) is proposed to address these issues. The CREMG integrates a planetary gear system and dual one-way bearings. The one-way bearings convert irregular bidirectional pendulum motion into unidirectional rotation, and the planetary gear system amplifies the rotation by a 1:4 transmission ratio, collectively enhancing energy conversion efficiency. Experimental results show that the proposed CREMG delivers a maximum RMS power of 304.46 mW at an optimal load resistance of 5000 Ω, with a 1 F capacitor charged to 3.44 V within 400 s, corresponding to a harvested energy of 5.92 J. To further validate its practical potential, the CREMG was used to power a customized wireless sensing circuit for temperature and humidity monitoring under random excitations. Overall, this work demonstrates a compact and efficient solution for low-frequency wave energy harvesting, offering a viable pathway toward self-powered marine sensing and autonomous ocean monitoring systems.